Do you think that a musician giving a performance can be compared to a salesman trying to sell you a something? When you perform at a recital or somewhere, don't you try to play "convincingly"? It seems to me that getting the audience to "buy" your performance is much the same as the salesman trying to sell you on his product. And what does your audience get when they are buying what you hold out for them? Do spend much time thinking about what kind of value you offer for price your listeners pay? Even when the ticket is free, listeners are giving their time. Finally, what is the worst possible mistake for a performer? Fatigue or boredom in the audience?